Assuming you are using the term "PCI-E" to mean a 64-bit parallel PCI-X card, this question is mostly to do with what your motherboard can accept and what drivers are available. If you have unused parallel PCI slots, then by all means use the Lacie card to give you FW800. If the Lacie card is 32-bit, it should nevertheless plug into and work in a 64-bit slot. You will need the correct drivers for the mode of operation you want to run in.

This is not directly an application program (a DAW in this case) issue. It's unlikely that there are many 64-bit parallel PCI device drivers for 64-bit DAWs.

You can get simple cable adaptors that plug into FW800 ports to take FW400 devices.

If, however, by "PCI-E" you are meaning your motherboard has only PCIe slots (serial PCI), a parallel card will not plug in at all, and your Lacie card stays on the shelf.

Bos , What I am asking is :
Is it more beneficial to use a PCI-e Firewire card over a PCI FW card ( not PCI-X).
My ASRock mb has a PCI-e slot in addition to 3 PCI slots available.
At what point does a bottleneck occur in either format ?
IF track counts exceed a certain total will two way communication of these gets choked?

I know the physical differences between PCI / PCI-e / PCI-X card connectors. The particular Lacie card is compatible for pci AND pci-x
but my MB ( ASRock z77 Pro 4 ) does not utilize PCI-X.

To address your 32 /64 bit reply:
So there is no need for concern when using a 32 bit PCI slot even though the DAW software is running at 64 bit ?

It depends on the motherboard design. It's very likely that all your parallel PCI slots are connected to one I/O sub-system, whereas each PCIe slot has its own route into the main chipset. This would not necessarily be a bottleneck if you do not have other high-speed parallel cards in operation at the same time as the FW card.

The Lacie card itself has the constraint of routing all its FW streams through a single PCI interface, so if you had a FW audio interface and a FW disk drive running together through the Lacie card, the PCI section of it could be a bottleneck, but it would apply to PCI serial as well as PCI parallel.

This hardware routing does not affect use of a 64-bit OS and DAW, providing the respective drivers are available. Most of the problems I have seen audio users running into with 64-bit OS versions boil down to the lack of functional 64-bit drivers for each bit of hardware they want to use.

As suspected thanks. Looks like I am good to go since I will have no other PCI cards installed except the Lacie FW.
The PC was built specifically for DAW w/ some video use, no other applications( i.e Internet etc) will be used on this strictly recording studio machine.